The present invention relates to bandwidth reservation in data networks, in particular for transmitting multimedia data in computer networks such as the Internet.
The Internet makes broad use of the connection-oriented protocol TCP/IP which, in turn, uses the underlying Internet Protocol, IP for short. IP, for its part, is a datagram protocol whose datagram property allows for it to be administered and scaled very easily and has, therefore, made an important contribution to the success of the Internet. However, a datagram protocol, such as IP, in particular, has the drawback that an assurance for a transmission is given neither generally nor in a particular volume of data in a particular time. This is called “best effort”, on the basis of which each network node makes the best possible attempt to forward the data pockets, which dispenses with a guaranteed level of reliability. Where the latter is required, a protocol in the layer above, such as TCP/IP, therefore provides a reliable connection using repetitions, state messages and time sequences. For the majority of applications to date, this improvement is sufficient. Such an assurance is referred to as quality of service. Accordingly, TCP/IP provides the quality of service that the messages are actually received and are received in the order of sending so long as the underlying layer is actually working; i.e., the connection is not signaled as being faulty.
The transmission of telephony and, in particular, moving pictures requires a further quality for the transmission, however. In particular, this includes the data being transmitted within a particular time. In the knowledge of this maximum delay time, the receiver is able to set up an adequate buffer and, thus, to ensure smooth display of moving pictures.
This improvement in the transmission assurances in networks is examined under the headword “Quality of Service”. As an overview combining the general knowledge of the person skilled in the art in this field, mention may be made of the book by P. Ferguson and G. Huston, “Quality of Service”, Wiley & Sons 1998 (ISBN 0-471-24358-2).
To reserve such connections on the Internet, the protocol RSVP is provided, which is described in the document “Resource Reservation Protocol (RSVP)” by R. Braden et al., RFC 2205, September 1997. RSVP is responsible only for setting up the reservation. To specify the operating parts themselves, in this case the quality of service, RSVP in principle allows the use of a number of protocols; for example, the protocol described in the document “Specification of Guaranteed Quality of Service” by S. Shenker et al., RFC 2212, September 1997. This document describes the operating parts to be reserved using parameters of the “token bucket” model.
Studies in this area also have been published in the article “Efficient Support of Delay and Rate Guarantees in an Internet” by L. Georgiadis et al., SIGCOMM 1996, pp. 106–116. The “token bucket” model used therein was chosen as a largely unspecific model which is also intended to permit appropriate specification of data with a nonuniform data rate. Data with a nonuniform data rate are, in particular, video data compressed on the basis of MPEG2, where not only full key frames but also much smaller change frames are transmitted. In the absence of other rules, the reservation needs to be geared to the large key frames for such data streams.
It is an object of the present invention to make it possible to determine the parameters for reserving transport of, in particular, multimedia data in a better way than previously and to specify how the associated parameters are expediently interchanged.